The present invention relates to cardiac stimulation probes, more particularly to probes to be implanted in the coronary network of the heart to allow stimulation of the left atrium by an xe2x80x9cactive implantable medical device,xe2x80x9d as such devices are defined by the Jun. 20, 1990 Directive 90/385/CEE of the Council of the European Communities. Such devices include, for example, pacemakers, defibrillators and/or cardiovertors, including xe2x80x9cmultisitexe2x80x9d type pulse generators.
It is conventional to implant endocardiac probes for stimulating the right atrium or right ventricle via the right venous peripheral network. In contrast, the installation of permanent probes in a cavity of the left heart implicates large operational risks, for example, the risk of bubbles passing towards the cerebral vascular network, which is located downstream of the left heart.
To avoid such risks, therefore, left heart cavity stimulation probes are introduced through the coronary network, with the access to the input of the coronary sinus being done via the right atrium. Such probes are generally provided at the distal extremity with an electrode disposed facing the left ventricle. In addition or in the alternative, such probes can be equipped with an electrode disposed facing the left atrium.
It is an object of the present invention to obtain such a probe, equipped with an electrode for stimulating the left atrium. However, stimulation of the left atrium from the coronary network also raises a certain number of difficulties. First, the amplitude of the atrial signal is much lower than that of the ventricular signal, and it is necessary, during the detection of the atrial signal, to reduce to a minimum the parasites, such as noise or other interference, which could be superimposed on the useful signal.
Second, from a mechanical point of view, the external diameter of the probe must be essentially uniform, that is as uniform as possible, so as to minimize the difficulty of extracting the probe if it must be withdrawn. This is because the extraction of a probe from the coronary network is a much more delicate task than extracting an endocardiac probe introduced in the peripheral venous network.
In addition, the introduction of a probe into the coronary network, via the endocardiac paths, is a particularly delicate intervention, taking into account in particular the fact that the position of the stimulation points are very important. In the case of a pulse generator of the xe2x80x9cmultisitexe2x80x9d type, the stimulation points of the right and left cavities must be as far apart as possible to optimize the resynchronization of the several cardiac cavities.
This particular type of probe also must respond to certain precise criteria: first, there should be an axial internal channel for threading a stylet in the probe at the time of the implantation, in particular for locating the input of the coronary sinus. Second, there should be a minimization of the use of rigid elements which could impair the progression of the probe through the coronary network after the surgeon has found coronary sinus input and introduced the probe extremity therein. Third, and more generally, such a probe should be sufficiently close in its handling characteristics to the existing probes (e.g., installation by use of stylet, preformed or not preformed, under a visual monitor such as an x-ray or fluoroscope, etc.) so that it is accepted without difficulty by the surgeons who will have to implant it.
In addition, from a commercial point of view, it is desirable to rationalize the manufacture of such a probe in order to reduce its cost, which implies limiting the complexity of the stimulation electrode that is made out of carbon, which is a material difficult to machine, and designing the probe in manner that it can be constructed using traditional materials and assembly techniques, ensuring the reliability of the assembly, as well with regard to the tightness of the probe and its mechanical resistance over time.
Primarily, the present invention proposes to produce a left atrial coronary probe by utilizing the known technique of a tripolar probe (an annular or sectoral stimulation electrode straddled by two annular reference electrodes, the reference electrodes being connected together and connected to the same reference potential) in order to mitigate the aforementioned difficulty, namely the risk of detection of large interfering signals, taking into account that the amplitude of the atrial signal is much lower than the amplitude of the ventricular signal.
The article by Callaghan et al., Space Discrimination of Cardiac Signals, REM, Vol. 6, No 3, p.223, discusses the advantage of the tripolar probe detection applied to the detection of an atrial endocardiac electrogram. This technique obtains a signal-to-noise ratio that is greater than what is possible to obtain with a conventional unipolar or a bipolar detection. The tripolar probe configuration also is described in EP-A-0 159 753, applied to the case of endocardiac or pericardial electrodes.
The present invention is broadly directed to a coronary stimulation probe for the left atrium which is a tripolar probe having a cylindrical body and a distal end. A stimulation electrode is provided, in an electrode area located axially and remotely of the distal end. The stimulation electrode is preferably annular or sectorial and electrically connected to a first conductor of the probe. The probe also is provided with two annular reference electrodes in the same electrode area, one distal and one proximal, which are connected electrically together and to a second conductor of the probe. The stimulation electrode is disposed axially between the two reference electrodes on the same probe axis. Moreover, the probe preferably comprises a first electric connection body connecting the two reference electrodes to an internal conductor segment that is disposed internally in the area of the stimulation electrode, but electrically isolated therefrom.
In one embodiment, the first conductor and the second conductor of the probe can be coaxial conductors. In one implementation of coaxial conductors, the small diameter or internal conductor is the first conductor connected to the stimulation electrode and the large diameter or external conductor is the second conductor connected to the two reference electrodes.
According to a certain number of advantageous subsidiary characteristics applied to this embodiment, the first electric connection body preferably comprises an electric connection between a first radial area in its periphery, the large diameter conductor, and a second radial area nearer to the axis of the probe (i.e., having a smaller dimension than the first radial area on the same axis of the probe), which is connected to the internal conductor segment. It can more preferably comprise a first part with a tubular body carrying one of the two reference electrodes, this tubular body having two diametrically opposite branches extending in an axial direction and carrying between them a core to which they are mechanically and electrically connected. The core is preferably connected to the other of the two reference electrodes by the aforementioned internal conductor segment disposed in the area of the stimulation electrode.
The probe also may comprise a second electric connection body, comprising an electric connection between a first radial area in its periphery, connected to the stimulation electrode, and second area radially nearer to the axis of the probe (i.e., smaller in dimension than the first radial area on the same axis), connected to the small diameter conductor. The probe also can in particular comprise the second electric connection body having a tubular body carrying the stimulation electrode on its surface. This tubular body can have two mechanically diametrically opposed branches extending in an axial direction along the probe axis, which branches are electrically connected together and to the small diameter conductor of the probe. In such an embodiment, the respective two branches of the two electric connection bodies can be oriented to extend axially in opposite directions and angularity shifted approximately 90xc2x0 so as to allow an interpenetration of the two bodies without contact therebetween. Further, the respective pairs of branches of the two bodies in the area of interpenetration can be maintained remotely from one another and electrically isolated by a joint molded in place, with possibly also a spacer made of an electrically insulating material to maintain the respective pairs of branches non- contacting in the area of interpenetration.
In one advantageous embodiment, the external diameter of the probe is essentially uniform and constant, without any extra thickness in the area of the electrodes.
In another advantageous embodiment, the probe comprises an axial internal channel continuously extending from the proximal extremity up to a point located beyond (i.e., distally of) the aforementioned area of the tripolar electrodes.
The internal conductor segment is preferably a deformable segment over least a part of its length.
In addition, the probe can comprise a collar carrying a steroid agent, assembled in an area located in the vicinity, in the distal direction, of the electrode area.